1. Field of the Invention
The present invention relates to a semiconductor substrate having a semiconductor layer in which strain is induced and a method of manufacturing the same, and to a semiconductor device using the semiconductor substrate and a method of manufacturing the same.
2. Description of the Related Art
Semiconductor devices have improved in performance so as to attain high-speed operation, low power consumption, and high integration because of progress in miniaturization of their minimum processing size. Lately, in order to increase operating speed, studies have been made of improving carrier mobility in the channel part of a transistor by employing a SiGe film and using the heterostructure of a Si film and the SiGe film or the properties of the SiGe film itself.
With respect to n-type MOS (Metal Oxide Semiconductor) or n-MOS transistors, it has been proposed to form a heterostructure having a SiGe film and a Si film epitaxially grown in the (001) plane direction thereon and induce tensile strain in the Si film by applying tensile stress to the Si film from the SiGe film using the fact that the SiGe film has a greater lattice constant than the Si film. It is known that electron mobility in the strain direction is better in such a Si film in which tensile strain is induced so that the performance of the n-MOS transistor can be improved by using such a Si film as a channel.
Further, with respect to p-type MOS (p-MOS) transistors, it has been proposed to form source and drain regions of SiGe in part of the surface of a SiGe substrate having a Ge concentration of 20-30% or a Si substrate and apply compressive strain to the channel of the Si film from both regions. It is known that such a configuration improves the hole mobility of the Si film so that the performance of the p-MOS transistor can be improved.
Further, in order to improve the performance of transistors, there has been proposed a so-called strained SOI (Silicon On Insulator) substrate, or a substrate in which the technology of SOI having a thin Si film for suppressing the parasitic capacitance and the short channel effect of transistors and the above-mentioned strain technology are merged.
According to one method of forming an SOI substrate in which strain is induced in a thin Si film, a SiGe film is caused to grow on a Si substrate, and a buried oxide film is formed at the interface between the Si substrate and the SiGe film by oxygen ion implantation and high temperature heat treatment using SIMOX (Separation by Implanted Oxygen) processing. Then, a Si film is formed on the SiGe film, and tensile strain is induced in the Si film (see Non-Patent Documents 1 and 2 described below).
According to another method, a thick SiGe film is caused to grow on a Si substrate by epitaxial growth, and the strain of the SiGe film is relaxed by heat treatment. A Si film is formed on the SiGe film, and tensile strain is induced in the Si film by the SiGe film, so that a strained Si film is formed. Then, hydrogen ions are implanted to a predetermined depth in the SiGe film under the strained Si film. Then, a separately prepared Si substrate having a thermal oxide film formed on its surface (Si substrate/thermal oxide film) is stuck to the substrate on which the strained Si film is formed. The SiGe film/strained Si film is separated by cleaving from the region in which the hydrogen ions are implanted, and the SiGe film is removed so that the strained Si film is exposed, thereby forming a strained SOI substrate of Si substrate/thermal oxide film/strained Si film (see Non-Patent Documents 3 and 4 described below).
[Non-Patent Document 1] S. Fukatsu et al., Appl. Phys. Lett. 72, pp. 3485 (1998)
[Non-Patent Document 2] T. Tezuka et al., Jpn. J. Appl. Phys. 40, pp. 2866 (2001)
[Non-Patent Document 3] K. Rim et al., IEEE IEDM Tech Dig., pp. 49 (2003)
[Non-Patent Document 4] C. Maleville et al., Ultra-Thin SOI and Strained Silicon-on-Insulator, Fabrication, Metrology, and Defects (SEMI Standard Technical Education Program, SEMICON West 2003, San Francisco, Jul. 15, 2003, USA)
However, according to the methods of Non-Patent Documents 3 and 4, the surface of the SiGe film should be smoothed in order to cause smooth crystal growth of the strained Si film. Further, since the cleavage surface of the SiGe film is uneven, planarization by CMP (chemical mechanical polish) is required. However, the strained Si film formed under the SiGe film is at most approximately 20 nm in thickness, and it is extremely difficult for CMP to achieve both surface flatness and uniform thickness of the strained Si film of approximately 20 nm in thickness, thus causing the problem of an extremely low yield. This results in a problem in that the cost of manufacturing an SOI substrate is extremely high.